1. Field of the Invention
The present invention relates to a manufacturing method of a vacuum airtight container. More particularly, the present invention relates to a manufacturing method of a vacuum airtight container which is used in a flat panel image displaying apparatus.
2. Description of the Related Art
In recent years, sizes of screens to be used in image displaying apparatuses become larger. Conventionally, although CRTs (cathode-ray tubes) were the mainstream of the image displaying apparatuses, there was a problem that the CRT is large in size and heavy in weight. Consequently, a light and thin flat panel image displaying apparatus (called an FPD (flat panel display) hereinafter) has attracted attention.
In this connection, the FPD which is bright and contrasty, has a wide field angle, and can cope with demands of wider screens and higher definition has been developed.
In various types of FPDs which have been actively researched and developed in recent years, there is an LCD (liquid crystal display). In addition, a PDP (plasma display panel), an organic EL (electroluminescence) panel and the like have been developed.
The principle of light emission in the FPD is different from that in the CRT. However, on another front, an FPD which causes a fluorescent member to emit light by using an electron beam as well as the CRT has been developed.
Here, it should be noted that the FPD of this type includes an FED (field emission display) which is a display of a type of emitting electrons via an electric field by using as an electron source a cold cathode instead of a hot cathode. Further, as one kind of FED, there is a display that SCEs (surface-conduction electron emitters) are arranged in a matrix on a glass substrate. The display of this type, which is called an SED (surface-conduction electron emitter display), was proposed by the applicant of the present application {for example, see Japanese Patent Application Laid-Open No. S64-031332 (called a document 1 hereinafter) and Japanese Patent Application Laid-Open No. H07-326311 (called a document 2 hereinafter)}.
Since each of the FED and the SED uses electron beams, it is necessary to maintain a high vacuum inside the container, as well as the CRT. That is, a deterioration of vacuum (that is, an increase of pressure) influences image quality and a lifetime of the electron source.
In order to obtain a vacuum container of which vacuum is maintained excellently, a method of heating the inside of the container as exhausting it, and sealing the container after discharging the gas adsorbed to the inner surface of the container is conventionally used (this heating process is called a “baking process” hereinafter). Further, in order to maintain the vacuum of the container after the sealing, a method of disposing a metal thin film called a getter inside the container, and exhausting the container by using a gas adsorption action of the getter is conventionally used.
Roughly, the getter is classified into two kinds, that is, an evaporation getter and a non-evaporable getter (called an NEG hereinafter).
In the evaporation getter represented by Ba, a metal film evaporated to the inner surface of the container in vacuum is used as a pump as it is.
The evaporation getter is characterized in that a pump function can be exerted immediately after the evaporation process. On the other hand, since a getter film once evaporated cannot be exposed in the atmosphere, the processes from the evaporation process to the sealing process have to be consistently performed in vacuum. Further, in the evaporation getter, some kind or another energy means (a power conducting source, a high-frequency power source, or the like) other than heat in the baking process is typically necessary for the evaporation process.
On the other hand, in the NEG, a metal such as Ti, Zr or V or an alloy mainly consisting of Ti, Zr and V is formed on the inner surface of the container by evaporation, sputtering or the like. Here, the NEG is characterized to be able to be exposed in the atmosphere after it was formed. However, the NEG once exposed in the atmosphere cannot exert the performance as the pump. For this reason, it is necessary to heat the NEG in vacuum so as to obtain a temperature equal to or higher than the temperature at which the NEG exerts adsorption performance. The NEG can first exert the performance as the pump via such a heating process.
The above heating process for the NEG is called “activation”. If the energy means such as the power conducting source, the high-frequency power source or the like is used as the heating means for activating the NEG, the activation can be selectively performed at arbitrary timing. Further, if an activation temperature is equal to or lower than a baking temperature, the NEG can be activated by the heat in the baking process. If the NEG can be activated by the heat in the baking process, specific means and process for activating the NEG can be omitted. Thus, it is desirable from the aspect of tact and cost.
In case of baking the vacuum container for the FPD (that is, in case of heating the container as exhausting it), since a conductance of exhaust is small because the container is thin, there is a possibility that the internal pressure of the container increases during the baking. More specifically, if the internal pressure of the container increases in a high-temperature state during the heating, there is a possibility in the FED and the SED that the electron source deteriorates. Thus, it is undesirable.
On the other hand, in a case where the NEG adopted as the getter is activated at the baking temperature, a gas discharged in the baking process is adsorbed (exhausted) by the NEG after the NEG was once activated. Consequently, since the pressure in the vacuum container decreases in the baking process, it is possible to suppress deterioration of the electron source due to the baking, and it is also possible to decrease the pressure in the vacuum container before the sealing is performed.
However, the operation that the discharged gas in the baking process is exhausted by the NEG implies that the NEG deteriorates in the baking process. Consequently, since the exhaust performance after the sealing, which is an essential object of the NEG, decreases, lifetime shortening or performance deterioration for each of the FED and the SED occurs.
To cope with such inconvenience, a technique for independently providing a getter to improve the pressure in the container in the baking process and a getter to be used to maintain the lifetime and the performance of each of the FED and the SED after the sealing is conventionally adopted.
Here, Japanese Patent Application Laid-Open No. 2001-076650 (corresponding to European Patent Application Publication EP 0996141A; called a document 3 hereinafter) discloses a method of providing an NEG within an image displaying area and further providing an evaporation getter or an NEG on the periphery of the image displaying area (this getter is called a peripheral getter hereinafter). However, in the document 3, in a case where the evaporation getter is adopted as the peripheral getter, a specific means (external energy) is necessary in order to evaporate the evaporation getter after activating the NEG in the image displaying area in a baking process. Moreover, in a case where the NEG is adopted as the peripheral getter, an NEG of the same kind as that of the NEG in the image displaying area (having the same activation temperature) or an NEG having an activation temperature higher than the temperature of the baking process is used.
If the kind of peripheral NEG is the same as that of the NEG in the image displaying area (namely, having the same activation temperature), both the peripheral NEG and the NEG in the image displaying area can be activated in the baking process. However, in such a case, since the peripheral NEG adsorbs the discharged gas in the baking process, the performance of the peripheral NEG deteriorates. Of course, the peripheral NEG can be later activated again. However, in this case, since a specific means (external energy) is necessary to do so, a new process occurs.
On the other hand, if the NEG having the activation temperature higher than the baking temperature is adopted, deterioration of the peripheral NEG in the baking process can be eliminated. However, even in this case, since a new means (external energy) is of course necessary for activation, a new process is necessary just the same.
Further, Japanese Patent Application Laid-Open No. H09-320493 (corresponding to French Patent Application Publication FR A1 2771549; called a document 4 hereinafter) discloses a method of providing two kinds of getters in a getter box provided in connection with a container. However, in the document 4, since one of these getters is the evaporation getter, a new means (external energy) and a new process for evaporation are necessary.
Furthermore, Japanese Patent Application Laid-Open No. H10-064457 (corresponding to European Patent Application Publication EP 0817234A; called a document 5 hereinafter) discloses a method of providing two kinds of NEGs respectively having different activation temperatures in a space provided in connection with a container. However, in the document 5, although the NEG having the lower activation temperature is activated in the baking process, it is necessary to selectively activate the NEG having the higher activation temperature by external energy after a baking process and a sealing process ended. Consequently, a new means (external energy) for the activation and an activation process other than the baking process are necessary.
Furthermore, Japanese Patent Application Laid-Open No. 2000-311588 (corresponding to U.S. Pat. No. 6,559,596; called a document 6 hereinafter) discloses laminated two kinds of NEGs provided within a displaying apparatus. In the document 6, the provided NEGs are heated and thus activated.
Conventionally, on the premise that the two kinds of getters are provided, the method of improving, on one hand, the pressure in the container by adsorbing the gas discharged in the baking process, and of maintaining, on the other hand, the pressure in the container after the sealing excellently and over the long term is adopted. However, to activate or evaporate either one of these two getters, the external energy other than the heat in the baking process is necessary, and also the specific process to do so is necessary.